This invention relates in general to earth boring drill pipe, and in particular to the tool joints for connecting the sections of drill pipe together.
Deep wells such as for oil and gas are drilled with a rotary drill bit rotated by a string of drill pipe. The drill pipe is made-up of individual members, each about 30 foot in length. The members are secured together by a threaded connection, called a tool joint. The tool joints must withstand the normal torque encounted during drilling, and also provide sealing to prevent drilling fluid being pumped down the drill pipe from leaking out the joints. Leakage out the tool joints causes wear due to the abrasiveness of the drilling fluid, which would lead to early failure.
The tool joint is made-up of a pin member and a box member. The pin member has external threads and an external annular make-up shoulder. The box member has internal threads and a rim or face that makes up against the make-up shoulder. In conventional drill pipe, there is no internal shoulder in the box member for contact by the nose or face of the pin. When the tool joint members are made-up at the surface, normally they will be made-up to a torque that exerts a pressure that is about one-half the yield strength between the box face and pin make-up shoulder.
Should additional torque be encountered while drilling, such as due to the bit or pipe becoming stuck, it is possible for the yield strength of the pin and box to be exceeded. Consequently, it is very important to have tool joints with high torque withstanding abilities, preferably in excess of the drill pipe itself.